Collapsible shelf



FIG. 1 is a top perspective view of a collapsible shelf showing my newdesign, with the broken line showing of side supports for illustrativepurposes only and forming no part of the claimed design;

FIG. 2 is an enlarged front elevational view thereof;

FIG. 3 is a right side elevational view of FIG. 2;

FIG. 4 is a left side elevational view of FIG. 2;

FIG. 5 is a top plan view of FIG. 2; and,

FIG. 6 is a bottom plan view of FIG. 2.

The ornamental design for a collapsible shelf, as shown and described.